MESOPHILIC PERFORMANCE OF ATTACHED-FILM REACTORS SUBJECT TO LOW-TEMPERATURE STRESS

Mesophilic (37 degrees C) performance of attached-film anaerobic diges ters fed with dairy manure that had been subjected to law temperature (10 degrees C) stress was evaluated Two digesters packed with limeston e gravel, two with pieces cut from non-woven polyester matting, and tw o with no packing were subjected to a temperature cycle between 37 deg rees C and 10 degrees C. Two control reactors without packing were mai ntained continuously at 37 degrees C. All reactors were operated in th e upflow mode, and the reactors without packing operated similarly to upflow anaerobic sludge blanket systems. None of the reactors regained their original performance in terms of biogas and methane production characteristics or pollution abatement after the temperature cycle; ho wever the control reactors also showed a similar decline in performanc e during the period of study. The reactors with polyester packing and those with no packing had similar values for biogas productivity and y ield, while those with limestone packing had significantly lower value s. It was concluded that the lack of complete recovery of reactor perf ormance could not be attributed to the temperature cycle. Variability in the feed composition or uniform decline in microbial activity over the prolonged period of time for which the reactors were operational m ost likely contributed to this effect.